EP2330405A1 - Method and device for measuring flow resistance parameters - Google Patents

Abstract

The method involves conveying fluid via a fluid flow element (24) using pumps (12) i.e. blood pumps, with a rotating conveying element i.e. rotor (2), where the fluid is in form of gas or liquid. The pumps have active regulating magnets i.e. permanent magnets, for bearing the conveying element. Pressure difference at the magnets is recorded and produced by the pumps at the rotor. A flow resistance parameter is determined under consideration of rotary speed of the conveying element. A volume stream is assigned to the detected load and rotary speed under consideration of type of the fluid. An independent claim is also included for a device for measuring the flow resistance parameter of a fluid flow element.

Description

The invention is in the field of metrology and relates in particular to the field of fluid mechanics.

Fluid mechanical measuring techniques and methods are basically known in a variety of configurations and applications. Corresponding measurements relate, for example, to the viscosity or, in reversal of this size, the flowability of fluids and the flow resistance or the resistance coefficient in the case of components through which a fluid can flow. Also, dynamic parameters such as the inertia of the liquid column in a component or the elasticity of the wall of the component with time-varying flow can be determined experimentally. Under a fluid is understood in this context, both a gas and a liquid.

Corresponding drag coefficients are characterized in the case of fluid-flow components by the flow direction, the pressure difference between points before and after flowing through the component, and the volume flow which is driven through the component by the corresponding pressure difference.

Accordingly, resistance coefficients can be reliably measured while measuring the corresponding physical quantities.

In many applications, however, it is not possible to measure the appropriate sizes, or you want to keep the measurement effort as low as possible. In addition, it is often difficult to gain access to the places where the appropriate sizes need to be measured.

In particular, in medical technology, if some of the fluid-flow elements are difficult to access or variable in their flow resistance, it is of great advantage if such a size as a flow resistance parameters can be measured with little effort in a short time, reliable and accurate.

Corresponding fluid mechanical measuring devices are known in principle.

From the DE-A-2919236 is a flow meter with a turbine wheel is known, which is stored in a regulated magnetic bearing.

From the U.S. Patent No. 6581476 B1 is known in a longitudinally flow-through tube built-rotor, which is in a special way axially magnetically mounted and by means of which both flow measurements and viscosity measurements can be performed. When carrying out viscosity measurements on a fluid flowing around the rotor, the power consumption of a drive of the rotor is measured as a function of the rotational speed. The determination of the viscosity is based on the friction between the cylindrical rotor surface and the liquid or within the moving liquid layers.

In addition, it is known from the cited document to measure an axial load on the rotor as a result of a relative movement of the rotor and to determine therefrom a viscosity variable.

In principle, however, the metrological applications of such a rotor relate only to the measurement of the fluids contained in it.

Against the background of the prior art, the object of the present invention is to provide a device and a method for measuring a fluid-permeable component which is not directly accessible. The measurement should be as simple as possible, feasible with little effort and the best possible result.

According to the invention, the object is achieved with the features of patent claim 1.

As a result, should be generated by this invention in a not yet completely known fluidically active component by the invention Pressure loss are measured in a fluid flow. This is done in principle by measuring the pressure loss, in particular the pressure loss as a function of the component flowing through the time constant or variable volume flow.

In order to avoid measurements in the immediate vicinity of the unknown component, the corresponding quantities are derived from variables which can be detected directly on a pump which drives the fluid flow. This pump is connected as directly as possible or via a negligible in their fluidic mechanical action pressure line with the element to be measured, and the pump is taken to promote the fluid in operation.

• Erstens kann die axiale Position des Rotors auf Mittenposition geregelt werden. Es wird ein Strom durch das Aktorelement geleitet, der die angreifende Kraft, also die Last, kompensieren kann. Durch Messung des Stromes als Stellgröße kann somit die Last der Pumpe berechnet werden. Zweitens kann die 1. Ableitung der Position (Axialgeschwindigkeit) auf 0 geregelt werden. Damit wird der Rotor durch Einspeisung eines geeigneten Stromes in eine Position verschoben, an der die Permanentmagnetkräfte des Magnetlagers die Lastkräfte kompensieren. An dieser Position ist der Steuerstrom nahezu 0. Diese Regelung ist unter dem Begriff Virtual Zero Power Control (VZP) bekannt. Durch Messung der Position als Zustandsgröße kann in diesem Fall die Last der Pumpe berechnet werden.

The unknown component, if the characteristics of the pump are known, can be fully characterized by measuring the volumetric flow and corresponding pump load values. The pump load values clearly correspond to the pressure gradient respectively generated in the pump and can be determined with little effort by acting on a corresponding conveying element of the pump forces. Such a conveying element is typically formed by a pump rotor, which is mounted according to the invention in a magnetic bearing. The pump rotor is radially passively centered by the magnetic bearing while its axial position is actively controlled. For this purpose, an integrated position sensor measures the axial rotor position. A controller determines a control current based on this measurement. The control current is passed through an electromagnetic actuator element. Thus, the axial rotor position can be changed selectively become. Basically, at least two methods for regulation are conceivable:

• First, the axial position of the rotor can be controlled to center position. A current is passed through the actuator element, which can compensate for the attacking force, ie the load. By measuring the current as a manipulated variable thus the load of the pump can be calculated. Second, the 1st derivative of the position (axial velocity) can be regulated to 0. Thus, the rotor is moved by feeding a suitable current in a position at which the permanent magnet forces of the magnetic bearing compensate for the load forces. At this position the control current is almost zero. This regulation is known as Virtual Zero Power Control (VZP). By measuring the position as a state variable, the load of the pump can be calculated in this case.

Both variables (current and position) are available in a pump of the type mentioned without further effort anyway, so that the additional measurement task can be additionally met with such a pump with the least effort.

To complete the measurement, only the speed or the energy consumption of the conveying element is needed, for example, in each case in order to determine a volume flow in dependence on the pump load.

The correspondingly measured quantities can be assigned the required quantities within a stored characteristic field or by an algorithm be considered, taking into account the nature of the fluid present.

The measuring device formed with the pump may therefore have to be calibrated for different fluids in order to form corresponding maps and / or algorithms.

For more accurate characterization of the flow-through element to be measured, the detection of rotational speeds or energy absorption values and pump loads or bearing forces at different rotational speeds may be advantageous.

The corresponding value pairs or groups of pairs of values or characteristic curves, which have thus been recorded by the measuring method according to the invention and the measuring device, can thus be used to reliably accurately correlate flow resistance parameters or resistance coefficients of a fluid-flow element downstream of the pump.

A particularly good characterization of the element to be measured can advantageously be made possible in that the measurements mentioned are carried out successively for different fluids.

The invention relates in addition to the measuring method described also to a device for measuring flow resistance parameters of a fluid-flow element, a corresponding pump, a first detection means for the rotational speed or energy absorption of the conveying element and a second detection means for the load of the pump and a Evaluation device, the at least one pair of values from a speed or energy intake and a pump load detected thereto assigns a flow resistance parameter.

The corresponding rotational speed of the conveying element can either be measured or, if the rotor can be driven by means of a synchronous drive, also be specified.

The load of the pump is advantageously measured by the registration of the bearing forces, in particular by detecting the necessary coil current for controlling a pump element actively controlling a bearing element magnetic bearing or the axial position of the rotor in the application of VZP.

For the assignment of corresponding flow resistance parameters to the detected measured values, the evaluation device advantageously has a memory device with stored characteristic diagrams for the rotational speeds and pump loads, in particular separately for different fluids.

Particularly advantageously, the invention is applicable to an axial flow pump which has a rotor mounted in a controlled axial bearing, which serves as a conveying element of the pump by means of conveying blades attached thereto.

By driving the rotor and the conveyance of a fluid in the axial direction, an axial force is generated in such an axial pump as a reaction force of the liquid acceleration, which is to be collected in the thrust bearing by corresponding magnetic forces. The axial position of the rotor is controlled by means of the current intensity of a coil, which in the stator of the bearing, in particular in addition to a permanent magnet, an additional magnetic force in response to the pump load generated to ensure a desired position of the rotor in the axial direction.

A corresponding axial pump is for example in the German patent application DE 101 23 138 B4 described together with an exemplary bearing control mechanism.

Thus, the method according to the invention and the device for measurement according to the invention also represent an inventive new use of a pump, which enables the task of measuring the difficult-to-reach, fluid-permeable component to be carried out with very little additional effort.

Fig. 1

schematisch in einem Längsschnitt eine Axialpumpe, die für das erfindungsgemäße Messverfahren bestimmt ist,

Fig. 2

ein Ablaufdiagramm, anhand dessen schematisch die Funktion des geregelten Magnetlagers dargestellt ist,

Fig. 3

schematisch die Auswertung der erfassten Messgrößen,

Fig. 4

eine Einrichtung zur Auswertung der Messungen sowie

Fig. 5

ein Kennfeld zur Auswertung der Messungen.

In the following the invention will be shown with reference to an embodiment in a drawing and described below. It shows

Fig. 1

schematically in a longitudinal section an axial pump, which is intended for the measuring method according to the invention,

Fig. 2

a flow chart, showing schematically the function of the controlled magnetic bearing,

Fig. 3

schematically the evaluation of the acquired measured variables,

Fig. 4

a device for the evaluation of measurements as well

Fig. 5

a map for the evaluation of the measurements.

Fig. 1 shows schematically in a longitudinal section a magnetic bearing axial pump, as for example as a blood pump for the human body application finds. The pump is inserted into a cylindrical tube 1 and has a rotor 2 with rotor blades 3 for propelling a fluid in the flow direction 4.

The drive for the rotor 2 provides a laminated core 5, windings 6 and yoke parts 7, 8, which together with the laminated core 5 form a highly permeable magnetic circuit which is closed by permanent magnets 9 in the core of the rotor 5, so that a total of a synchronous motor with outside lying stator is commutated electronically.

The rotor 5 is magnetically non-contact by means of permanent magnets 10, 10a, whose magnetic axis is aligned parallel to the flow direction 4, and stationary annular permanent magnets 11, 11a in the axial direction.

The permanent magnets 10, 11 and 10a, 11a are each aligned so that they attract in pairs in the axial direction. Thus, an unstable equilibrium is formed in the axial direction 4 at best, so that for non-contact storage additionally a control device must be provided. In the radial direction, an automatic centering of the rotor 2 is realized by the ring shape of the magnets 11, 11a.

For detecting the axial position of the rotor 2, in each case a sensor coil 14, 14a is provided in each of the stationary parts of the axial pump 12, 13 which extend in the extension of the rotor 2 within the tube 1, and a respective shorting ring 15, 15a is located within the rotor, so that by means of inductance the sensor coils 14, 14a respectively the distance to the respective short-circuit ring 15, 15a and thus the axial position of the rotor 2 can be measured.

The corresponding measured variables are fed as input variables to a control device which, depending on the measured position or on the difference from the target position of the rotor, controls a current through two control coils 16, 16a which strengthen or weaken the respective axial fields of the permanent magnets 11, 11a to control the attraction force of the permanent magnets 10, 11, 10a, 11a such that the rotor 2 is moved in the axial direction to its desired position, or to a position at which the current through the control coils is equal to zero (VZP).

If now the rotor 2 is set in rotation by switching on the rotary drive in such a way that a fluid located in the tube 1 is conveyed in the direction 4, the result is a reaction force which is opposite to the force acting on the fluid in the direction 4 and Rotor 2 temporarily deflects axially.

This process is closer to the Fig. 2 described in which the in the Fig. 1 already shown elements in accordance with the same reference numerals.

The drive control is in the Fig. 2 denoted by 17 and acts on one in the Fig. 2 only very schematically illustrated drive winding 18, which sets the rotor 2 in rotation. If it is a synchronous motor, a speed can already be predetermined with the drive control 17. Is it? around a sensorless brushless DC motor, the speed of the induced back voltage can be determined. Otherwise, a speed sensor for measuring the speed can additionally be provided in the area of the rotor 2.

When the rotor 2 is rotated, the fluid flows as shown in FIG Fig. 2 is represented by the arrows 19, 20, 21, 22 and 23, through the tube 1 and its continuation. The fluid-flow element to be measured in the illustrated case is denoted by 24 and, in the specific case illustrated, constitutes an apertured diaphragm which offers a certain resistance to the fluid flow which is to be measured. Of course, this example is only to be regarded as schematic and stands for any fluid-flowable elements which can also be made considerably more complex.

It is only essential in the representation of the invention that the flow resistance parameters of the element 24 can be determined exclusively by detecting measured variables in the region of the axial pump.

During operation of the pump drive as shown above, a force results on the rotor 2, which is directed in the direction of the arrow 25 and seeks to reduce the axial gap to the stationary component 12. The size of this gap is in the Fig. 2 designated by the reference numeral 26, while the deviation of the rotor position from the center position / target position of the rotor is denoted by 27. This deviation is detected by means of the sensor 28, which transmits this quantity to the control device 29 for the axial position of the rotor. These Control device accordingly determines the necessary current i through the control coil 16, which influences the axial magnetic field acting on at least one of the permanent magnets in the rotor 2.

In this way, the axial position of the rotor is controlled and held stable in the center position.

The current intensity i necessary for the modulation is a measure of the counterforce acting on the rotor 2 or the pump load or also the pressure difference in the pumped fluid produced by the pump.

Alternatively, by feeding a suitable current i through the control coil 16, the rotor can be moved to an axial position at which the permanent magnetic forces completely compensate for the applied force. At this position, the current i becomes close to 0. The deviation 27 from the central position of the rotor can be detected by means of the sensor 28 and is a measure of the counterforce acting on the rotor 2 or the pump load or also the pressure difference in the pumped fluid. This method, as introduced earlier, is called Virtual Zero Power Control (VZP).

In the Fig. 3 is shown schematically in a flowchart of the flow of the measurement, wherein first in a first step 31, the storage control is turned on and then in a step 30, the drive is started. In a further step 32, the control current required for the axial stabilization for the bearing control or the axial rotor position is measured, and in a step 33, the rotational speed of the pump drive is detected. These values will be in a next one Evaluation step 34 associated with a characteristic diagram in consideration of the known toughness of the fluid a flow resistance parameter of the unknown element 24, and this is output in an output step 35.

To determine dynamic flow resistance parameters such as inertia of the liquid column and elasticity of the component wall, a dynamic speed stimulation signal must be used instead of a stationary speed. The pump load and the volume flow are each calculated using the speed information and the determined disturbance force. The required parameters can be determined using system identification methods.

Based on Fig. 4 the structure of the measuring device shall be shown below.

Therein, 36 denotes the current intensity sensor necessary for the axial bearing stabilization, 36 alternatively, in the case of using a virtual zero power control control system, may also designate the axial rotor position sensor; 37 denotes a rotational speed sensor of the rotor 2 or a sensor for power consumption. The sensors are connected to the evaluation device 38, which has a comparison device 39 and a memory device 40. In the memory device 40, the corresponding maps for speed and current or position values are stored. The evaluation device 38 also controls the drive 17 of the rotor. In addition, the evaluation device 39 can receive information about the type or viscosity of the fluid used via the input unit 41.

Subsequent to the comparison process, the evaluation device 38 outputs the determined flow resistance parameter to an output device 42.

Instead of comparing measured values with a characteristic field, the evaluation can also be carried out by calculation using an evaluation algorithm.

In the Fig. 5 schematically a map is shown in which each rotational speeds are plotted on the x-axis and corresponding currents of the control coils for the axial stabilization of the rotor on the y-axis. Each solid graph indicates the relationship between speed and current at a particular, downstream of the pump flow element with a defined flow resistance. The higher the flow resistance of the downstream fluid-flow element, the more the axial force increases on the bearing of the rotor. At the same rotational speed of the rotor, the measured value 43 means a higher flow resistance of the element to be measured than the measured value 44, since the backflow to the axial pump and thus the axial force on the bearing is stronger. In this way, by assigning the pair of measured values to a specific characteristic curve of the field, after appropriate measurement, a flow resistance parameter of an element to be measured can be determined. Similarly, you can use the axial position instead of the current when using VZP.

The invention thus allows, with minimal additional measures on an axial pump their use as a measuring device for the measurement of fluidic Characteristics of a difficult-to-access element to be connected to the pump.

Claims (13)

Method for measuring one or more flow resistance parameters of an element through which a fluid can flow, in which fluid is conveyed through the element by means of a pump (2, 12, 13) with a rotating delivery element (2), the pump having an actively controlled magnetic bearing (10, 10a, 11, 11a, 16, 16a) for supporting the conveying element (2) and wherein the pressure difference ("load") generated by the pump above the rotor is detected at the magnetic bearing and determined therefrom in particular taking into account the rotational speed of the conveying element of the flow resistance parameters , A method according to claim 1, characterized in that at least one of the flow resistance parameters is determined successively for different rotational speeds of the conveying element (2). A method according to claim 1, characterized in that the flow resistance parameters are determined by measuring the response to suitable dynamic test signals for the engine speed. A method according to claim 1, 2 or 3, characterized in that the detected load and the detected speed taking into account the nature of the present fluid based on a stored map or an algorithm is assigned a volume flow. A method according to claim 1, 2, 3 or 4, characterized in that the detected load and the detected speed, taking into account the type of fluid present on the basis of a stored map or an algorithm, a flow resistance parameter of a fluid flowing through the element (24) is assigned. Method according to one of the preceding claims, characterized in that the measured variable is a current strength of a magnetic field generating coil (16, 16 a). Method according to one of the preceding claims, characterized in that the measured variable is an axial displacement (27) of the rotor from its center position. Method according to one of the preceding claims, characterized in that the flow resistance parameter for at least two different fluids is determined. Device for measuring a flow resistance parameter of a fluid-flow element (24) with a connectable to the element, an actively controllable magnetically mounted rotary conveyor element (2) having pump (2, 12, 13), a first detection means (36) for the speed or the energy consumption of the conveying element, a second detection device (37) for the load of the pump and an evaluation device (38), the at least one Value pair assigns a flow resistance parameter from a speed and a pump load detected thereto. Device according to claim 9, characterized in that the evaluation device (38) has a memory device (40) with stored maps for rotational speeds and pump loads. Device according to claim 9 or 10, characterized in that the second detection device (37) the load as a measured variable of the magnetic bearing (10, 10a, 11, 11a, 16, 16a) of the conveying element (2) or one with this measured variable in a unique manner coherent size recorded. Device according to claim 9, 10 or 11, characterized in that the pump is an axial pump with an axially in a magnetic, actively controlled thrust bearing (10, 10a, 11, 11a, 16, 16a) mounted rotor (2). Use of a fluid pump, which has a rotating delivery element (2) and an actively controlled magnetic bearing for the delivery element, for measuring a flow resistance parameter of a fluid-permeable element according to a method according to one of claims 1 to 8.

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